jQuery / Javascript 代码检查，如果不是未定义
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jQuery / Javascript code check, if not undefined
提问by Jeremy
Is this code good?
这段代码好吗？
var wlocation = $(this).closest('.myclass').find('li a').attr('href');
if (wlocation.prop !== undefined) { window.location = wlocation; }
or should I do
或者我应该做
var wlocation = $(this).closest('.myclass').find('li a').attr('href');
if (wlocation.prop !== "undefined") { window.location = wlocation; }
回答by Diego
I like this:
我喜欢这个：
if (wlocation !== undefined)
But if you prefer the second way wouldn't be as you posted. It would be:
但是，如果您更喜欢第二种方式，则不会像您发布的那样。这将是：
if (typeof wlocation !== "undefined")
回答by jeremy
I generally like the shorthand version:
我通常喜欢速记版本：
if (!!wlocation) { window.location = wlocation; }
回答by Bruno
$.fn.attr(attributeName)returns the attribute value as string, or undefinedwhen the attribute is not present.
$.fn.attr(attributeName)将属性值作为字符串返回，或者undefined当属性不存在时。
Since "", and undefinedare both falsy(evaluates to false when coerced to boolean) values in JavaScript, in this case I would write the check as below:
由于"", 和在 JavaScriptundefined中都是假的（当强制为布尔值时计算为假）值，在这种情况下，我将编写如下检查：
if (wlocation) { ... }
